1. Field of the Invention
The present invention relates to an airbag system for automotive vehicles, and more particularly to an inflating assembly for an airbag system using a projectile launched by ignition of a propellant and having improved performance for blowing out the gas.
2. Description of the Prior Art
Airbag systems for automotive vehicles have undergone significant development efforts in recent years due to an increased awareness as to their effectiveness. These airbag systems are typically activated upon receipt of a signal from an appropriate detector or sensor which indicates that inflation of the airbag is required. A variety of inflators are used by these systems to expand the airbag in a manner which provides certain advantages. Many systems initiate inflation by removing an isolation between the airbag and the inflator. Thereafter, some inflating medium, whether it may be pressured gases, gases generated by combustion of a propellant, a mixture thereof, or other suitable fluids, is supplied to the airbag.
A portion of the development efforts for airbag systems has concentrated upon controlling the flow from the inflator to the airbag after inflation has been initiated. In order to provide a reliable airbag system, not only there must be a sufficient flow of the inflating medium to the airbag in a timely manner, but the airbag must remain structurally intact throughout operation. As one proposed alternative for achieving these two fundamental objectives, the propellant-type airbag system that gases generated by combustion of a propellant are supplied to the airbag has been developed.
However, this type system suffers from many deficiencies, since filtering devices for controlling flow from the inflator to the airbag and lowering the temperature of gases generated by combustion are required. For instance, the filtering devices may not retain all the particles generated upon activation of the inflator. Consequently, some particles may pass through the filtering device to restrict the flow to the airbag or some may enter the airbag. Both these cases may adversely affect performance of the airbag system. Even if the filtering device properly functions and retains all the generated particles, this may induce a further flow restriction to the airbag by blocking an entire passageway or a portion thereof. Moreover, cost of manufacturing and maintenance of the inflator is raised by using the filtering device.
As one proposed alternative for solving the above deficiencies, the inflator that employs a projectile to remove the isolating member has been developed. U.S. Pat. No. 3,788,667 to Vancil, issued Jan. 29, 1974, discloses a piston-like member to remove a barrier isolating the inflator from the airbag. U.S. Pat. No. 3,836,170 to Grosch et al., issued Sep. 17, 1974, discloses a blunt nosed projectile which tapers to a degree but not to a point.
However, the removal of the barrier by the blunt nosed projectile of Grosch et al. is not controlled. That is, the tearing pattern will typically vary dependent upon various factors. As a result of inconsistent and uncontrolled tearing of the barrier, operational performance of the airbag system is degraded, so that occupants may not be protected enough.
A large number of the airbag systems use two types of sources, typically a compressed gas which is stored at ambient temperature, i.e., a cold gas, and gases generated by combustion of a propellant, i.e., a hot gas. For instance, U.S. Pat. No. 5,273,312 to Coultas et al., issued Dec. 28, 1993, discloses releasing a stored gas by removal of an isolation and thereafter activating an inflator. More particularly, a longitudinal through hole extends through the piston which is employed as a projectile and therethrough hot products generated by combustion of pyrotechnic charge are transferred to ignite booster charge. By burning the booster charge, the body of pyrotechnic material is ignited to generate hot gases. The generated gases are mixed with a gas stored in a container. Score lines are formed on burst disk and it is ruptured with a predetermined pattern.